A multichromotropic dinuclear copper(II) complex: Unveiling its structural and spectroscopic properties

A novel dinuclear copper(II) complex, [Cu₂L₂(μ-Cl)₂]Cl₂•4H₂O, was synthesized using a tetradentate hemilabile ligand, 3,3′-((pyridin-2-ylmethyl)azanediyl)dipropanamide (L). The complex was characterized by various spectroscopic techniques, including FT-IR, UV-Vis spectroscopy, elemental analysis, TG-DTA, and conductivity measurements. X-ray crystallography confirmed the formation of the binuclear complex, revealing a dicationic unit with distorted octahedral geometry at the copper centers, bridged by two chloride ions. The coordination environment around each copper ion includes two nitrogen and two oxygen donors from the ligand, along with the bridging chlorides. Notably, the complex exhibits significant chromotropism, including solvatochromism, halochromism, ionochromism, and thermochromism, which are attributed to the Jahn-Teller effect and the flexible coordination environment around the copper centers. Thermal analysis indicates the stability of the complex up to 118°C, with subsequent decomposition occurring in distinct stages. Hirshfeld surface analysis further elucidates the intermolecular interactions within the crystal lattice. Computational studies were conducted using Time Dependent Density Functional Theory (TD-DFT) to gain insights into the nature of the observed chromotropism. The computed absorption spectra closely matched the experimental data, validating the proposed electronic transitions responsible for the chromotropic behavior. The multifaceted chromotropic behavior of this complex highlights its potential applications in sensing technologies and smart materials. The study advances the understanding of chromotropism in metal complexes and provides insights into the design of responsive materials based on transition metal chemistry.